The invention relates to an ion beam system for irradiating tumour tissues and to a method of operating the system, in accordance with the preambles of the independent claims.
From U.S. Pat. No. 4,870,287 there is known a proton beam system for the selective production and transport of proton beams from a single proton source, via an accelerator, to a plurality of patient treatment stations, each of the treatment stations having a rotatable drum structure, hereinafter referred to as a gantry. In the known system, that gantry delivers the proton beam at various irradiation angles to a patient, who is arranged in a fixed position on a patient couch. A summary of gantry systems by Pedroni is known, from xe2x80x9cBeam deliveryxe2x80x9d in Hadron Therapy in Oncology, Editors U. A. Maldi and B. Larson, Elsevier 1994, pages 434-452.
As long as such ion beam systems for irradiating tumour tissues operate with the lightest ion of the periodic system, namely the hydrogen ion or proton, the deflection magnets for a gantry and the masses of the latter are relatively small and manageable. However, when heavier ions such as the carbon ion, or others, are to be used, deflection magnets that are several times larger have to be used in order to direct the highly accelerated ions from the axis of a gantry to the periphery of the gantry and back to the gantry centre, where the patient is positioned. At the same time, correspondingly large masses have to be provided in the gantry as a counterweight to the deflection magnets, with the result that the rotating gantry structure, which has to be rotated and controlled with an accuracy of a few millimeters, weighs several hundred tonnes. As the ion mass number increases, so the gantry solution that has been favoured becomes heavier and less manageable and requires ever larger buildings for accommodating the treatment systems.
The aim of any beam therapy is to deposit as high a dose of radiation as possible in a narrowly circumscribed regionxe2x80x94the tumour volumexe2x80x94and, as far as possible, to spare the surrounding healthy tissue. In customary X-ray therapy, because of the exponential decay of the photon dose with the depth of penetration in the conventional subcutaneous beam therapy of relatively deep-lying tumours, a high localised dose can be achieved only by directing the beam at the tumour volume from several directions in an intersecting irradiation technique. As a result, the involvement of healthy tissue in front of and behind the tumour volume is reduced. In clinical practice, two or three entry angles are usual and, with an inverse dose plan in the case of intensity-modulated therapy using photons, up to nine or ten entry channels, that is to say irradiation angle positions, are often planned. Such multi-field irradiations are feasible especially using the known gantry systems.
In a manner analogous to such photon beam therapy, a plurality of entry ports are also desirable in ion beam therapy although, as a result of the inverted dose profile of the ion beams, the dose in the entry channel is smaller than the dose in the region of the tumour volume. However, distribution of the unavoidable entry dose over a plurality of irradiation angles would, in the case of ion beam therapy too, signify a further clinical advantage. The known ion beam systems for proton beam treatment are therefore provided with irradiation application from all directions by means of appropriate gantry systems.
The gantry systems known from the Patent Specification U.S. Pat. No. 4,870,287 to that extent correspond to the gantry systems from photon and X-ray therapy. They first deflect the beam away from the patient axis and then bend it back at 90xc2x0 to the patient. Variable irradiation angles are in that case achieved by means of the fact that the entire deflecting system is rotated through 360xc2x0 along the beam direction with the aid of the gantry. The mechanical rotation serves the purpose, above all, of not having to vary the settings of the magnets and of having only to carry out mechanical rotation. However, that advantage of simple mechanical rotation without variation of the settings of the electromagnets holds only for as long as the gantry system uses a divergent ion beam for treatment. When a concentrated pencil-thin ion beam is produced, however, with an active scanning system being used for scanning the tumour volume, the magnetic field is no longer constant and unvarying, because the beam energy and, as a result, the magnetic constancy have to be utilised in accordance with the requisite energy steps having to be used for that pencil beam.
As a result, the main reason for a gantry having fixed magnet settings is no longer present, especially as, for the scanning system, the pencil beam already has to be deflected in an X and Y direction orthogonal to the central ion beam deflection region.
Furthermore, experience with the proton beam therapy system known from the Patent Specification U.S. Pat. No. 4 870 287 shows that, in the case of ion beam therapy of deep-lying tumours, not all the possible radiation-entry angles of a gantry are used with equal frequency. Rather, it has been found that there is a large range of seldom used irradiation angle zones because frequently occurring kinds of tumour necessitate frequently recurring restricted angle settings of the gantry. To that extent it has been found that conventional gantry systems do not constitute optimum solutions-for ion beam therapy because a large portion of the possible irradiation angles of a gantry remain little-used.
It is characteristic of the known and planned ion therapy systems that the particle beam is directed through the gantry system at a fixed angle and variation of the angle can be achieved only mechanically, by rotating the entire system. Because of the high energy of the particlesxe2x80x94200 MeV for protons and approximately 400 MeV/U for carbon ionsxe2x80x94and because of the large-area apertures necessary for scanning of the ion beams, deflection magnets having a high magnetic field strength and large-area apertures are necessary. That means that the electromagnets reach considerable dimensions and weight. A barrel-shaped gantry for carbon ions is accordingly designed for a radius of 7 m and a length of 15-20 m and a weight of 300-400 t, of which about 50 t alone is attributable to a concrete weight acting as a counterweight to the magnets. In the case of such considerable weights, the tolerances of the bearings and, as a result, the positional accuracy of the beam become increasingly important. In the case of the patient, however, the tolerance limits are in the millimeter range. In the case of the gantry systems constructed hitherto, such tolerance limits are difficult to meet.
In the construction of ion beam systems for hospitals, the construction of a plurality of gantry systems is a significant cost factor. The costs relate to the gantry itself, at more than 15 million DM per system, and to the construction of suitable operational rooms of more than 14 m in height and width and more than 20 m in length, which means an enclosed space of more than 4,000 m3. Such rooms have to be shielded by thick-walled concrete. In addition, the planned use of ion scanning methods still constitutes an as yet unsolved problem with regard to the necessary mechanical precision. For that reason, in the case of an ion scanning method, the requisite precision of 1 mm has to be checked, verified and corrected after each setting and for each new treatment.
The problem of the invention is to overcome the disadvantages of the prior art for an ion beam system and to provide irradiation systems that, after reducing costs and saving space, meet the requirements with, at the same time, increased precision.
The problem is solved by the features of the subject-matter of the independent claims. Preferred developments of the invention are shown by the features of the dependent claims.
The solution to the problem is based upon the fact that the patient is fixed in a lying posture on a patient couch and this horizontal position is not changed before or during irradiation. This horizontal position on a patient couch has the advantage that uncontrolled organ movementsxe2x80x94of the kind that disadvantageously occur in the case of a sitting position or on rotation during treatmentxe2x80x94are avoided. That means that the apparatus provided for rotation of the patient couch is used solely for adjusting the irradiation angle but is not actuated during active irradiation. Accordingly, an irradiation angle for the lying patient can advantageously be composed of all possible angles (4xcfx80), with 360xc2x0 positioning (2xcfx80) of the horizontal patient couch on the irradiation plane being possible by virtue of the apparatus for rotation of the patient couch and, in addition, with positioning of the beam direction through 180xc2x0 (xcfx80) orthogonally thereto; that is to say, by means of the irradiation systems according to the invention, irradiation can be carried out from vertically above, and around the patient laterally, to vertically below. As a result, it is advantageously possible, in the case of the solution according to the invention, to dispense with a gantry that rotates through 360xc2x0; nor, because of the problem being addressed, is such a gantry desirable, because a gantry that rotates through 360xc2x0 restricts the space around the patient and as a result hinders access as well as the installation of diagnostic units such as, for example, a PET camera.
For that purpose, the solution according to the invention has, in addition to an apparatus for rotation of the patient couch about a vertical axis, at least one of the following irradiation systems: a first irradiation system having an asymmetrical scanning system of fixed location, which has a central ion beam deflection region for deflection angles of up to xc2x115xc2x0 with respect to the horizontal direction and makes possible scanning of a tumour volume in the central ion beam deflection region, and which has an additional lifting apparatus for the patient couch, and a second irradiation system, which has an ion beam deflection apparatus for a deflection angle range greater than the first irradiation system and a symmetrical scanning unit for scanning the tumour volume, which scanning unit is arranged downstream of the ion beam deflection apparatus and is arranged to pivot synchronously with the deflection angle of the ion beam deflection apparatus.
Preferably, the ion beam system has at least two first irradiation systems and a second irradiation system, each in a separate irradiation room. That preferred division between two irradiation systems having restricted deflection angles of up to xc2x115xc2x0 takes into account the fact that two thirds of tumour tissue treatments can be dealt with by using such an ion beam system and accordingly, in those irradiation systems having deflection angles restricted to xc2x115xc2x0, an asymmetrical scanning system, which in the X direction covers the width of the tumour volume and in the Y direction not only takes account of the depth of the tumour volume but also, as a result of enlargement of the defelction magnet system in the Y direction, extends the central ion beam deflection range to xc2x115xc2x0 and at the same time, in the region of the central ion beam deflection region, makes possible scanning the depth of the tumour volume. For that purpose, the patient couch is provided with a lifting means in addition to the rotating means in order that it can be positioned at the deflection angle or irradiation angle of the central ion beam deflection region. The remaining portion of approximately one third of patients, for whom larger central ion beam deflection regions are required, are-treated using a second irradiation system, which can, independently of a scanning unit, initially with the aid of external deflection magnet units, deflect the ion beam up to xc2x190xc2x0 with respect to the horizontal plane. A symmetrical scanning unit for scanning the tumour volume is pivoted synchronously with the deflection angle of the ion beam deflection apparatus of that second irradiation system, in the same direction as the deflection angle, so that the deflection magnet for such large deflection angles and the aperture of the magnet can be kept small and, likewise, the symmetrical scanning unit needs to be dimensioned only for deflecting and for scanning the tumour volume, which means a considerable saving in terms of weight and volume compared with the previously proposed gantry systems.
Because the preparation, and fixing in position, of the patient on the patient couch takes most of the time in the overall irradiation cycle in an ion beam system for irradiating tumour tissues, the ion beam system has at least one preparation room per irradiation system, each having a patient couch. Preferably, two or more preparation and aftercare rooms per irradiation system can be used. The number of requisite irradiation rooms accordingly increases with the number of irradiation systems used, and the number of preparation rooms increases with the time required for fixing a patient in position on the horizontal patient couch as a proportion of the actual irradiation procedure in the irradiation room.
Whereas, for an irradiation angle of between xe2x88x9215xc2x0 and +15xc2x0, only one asymmetrical scanning unit of the first irradiation system is required and, except for setting the lifting and rotation of the patient couch, only the excitation current for one of the deflection magnets of the scanning system has to be made available and an extended exit window for the ion beam from the asymmetrical scanning system has to be provided, there is used, in a preferred, embodiment of the invention for the second irradiation system, an ion beam deflection apparatus of fixed location having a variable deflection angle, which apparatus is arranged to the side of the patient couch, the patient couch having an additional lifting apparatus, which overcomes substantially greater height differences than the lifting apparatus of the first irradiation system. The deflection magnet required for those larger irradiation angles can, however, be provided with a smaller aperture because the pencil-shaped ion beam passes the deflection magnet without undergoing prior deflection by a scanning unit in the X direction. Only after deflection is there then connected an appropriately dimensioned symmetrical scanning unit, which is arranged to pivot together with the deflection angle so that again the entire tumour volume can be scanned within the central ion beam deflection region.
Alternatively to the ion beam deflection magnet arranged to the side of the patient couch, that magnet can also, in a further embodiment of the invention, be arranged vertically above the patient, and the patient couch can be provided, not with a lifting apparatus, but with an apparatus that is displaceable laterally in the horizontal plane. That preferred alternative embodiment of the invention also makes it possible, without a rotating gantry, for a large range of radiation angles to be available for treating tumours.
In a further preferred embodiment of the invention, the second irradiation system has an ion beam deflection apparatus, having a variable deflection angle, which is displaceable on a horizontal linear track, and the patient couch is fixed in all directions laterally. That means that the patient couch has neither a lifting apparatus nor a means of displacement in the two axes of the horizontal plane. Only rotation about the vertical axis is possible, in order to fix the patient couch in position at an appropriate angle of rotation with respect to the irradiation direction. The horizontal linear track, on which the ion beam deflection apparatus slides displaceably, can be arranged above or below the patient, the excitation current in the magnet at the same time varying together with the displacement in order to deflect the ion beam at various angles towards the patient fixed in position.
In a further preferred embodiment of the invention, the second irradiation system has an ion beam deflection apparatus of fixed location having a variable deflection angle and has an ion beam deflection apparatus, having a variable deflection angle, which is displaceable on a vertical linear track. The two variable deflection angles are so matched to one another that the patient couch can remain in a fixed position laterally and, despite a varying treatment angle, no lateral displacement of the patient couch is necessary. The scanning unit is arranged downstream of that ion beam deflection apparatus which is displaceable on a vertical linear track and can consequently be of completely symmetrical construction in order to scan the tumour volume. This solution has the advantage over horizontal displaceability of the ion beam deflection apparatus that, for the vertical linear track of the displaceable ion beam deflection apparatus, only the deflection magnet has to be provided with a lifting apparatus. Accordingly, whilst the patient remains in his fixed position without lateral displacement, for positioning of the ion beam, a second deflection magnet is, in this case, moved up and down using a lifting apparatus in order to vary the irradiation angle. Once the irradiation angle has been set, it remains unchanged and constant during irradiation; nor is the patient further moved during irradiation.
In a further preferred embodiment of the invention, the second irradiation system has an ion beam deflection apparatus that is linearly displaceable at an angle xcex1 with respect to the horizontal direction on a sloping linear track, for a deflection angle range of from xe2x88x92xcex1 to xe2x88x92(xcex1+90xc2x0), whilst the patient couch remains fixed in position laterally. For that purpose, the ion beam entering the treatment room horizontally is first deflected at an angle xcex1 towards the linearly displaceable ion beam deflection apparatus and that ion beam deflection apparatus, which requires only a linear displacement mechanism, directs the ion beam at the patient at a predetermined angle. That angle can range from 0 to 90xc2x0 and can also, in a corresponding alternative arrangement, be arranged from 0 to xe2x88x9290xc2x0. In the first case, the sloping linear track is oriented from beside the patient to above the patient and, in the other case, the sloping linear track, on which the ion deflection apparatus slides, is displaced from a position to the side of the patient to a position below the patient. As a result of such a second irradiation system and a linearly displaceable ion beam deflection apparatus, it is possible to dispense with the resource-intensive construction of a gantry, and the following advantages are essentially achieved:
1. greater mechanical stability because of the linear movement on a sloping plane compared to rotation of a gantry;
2. omission of compensating weights that are otherwise necessary;
3. comparatively lighter weights for all moving parts;
4. comparatively lighter dipole magnets because only small apertures are necessary;
5. reduction of the enclosed, shielded irradiation room to approximately 600 cm3, that is to say less than a quarter of the space for a rotating gantry; and
6. less restriction of the space around the patient couch and, consequently, improved possibilities for setting up other monitoring systems such as PET (photon emission topography device).
The same advantages can be achieved when, in a further preferred embodiment of the invention, the second irradiation system has an ion beam deflection apparatus of fixed location having a variable deflection angle and, in addition, an ion beam deflection apparatus which is linearly displaceable at an angle xcex1 with respect to the horizontal direction on a sloping linear track, for a deflection angle range of from xe2x88x92xcex1 to xe2x88x92(xcex1+90xc2x0), whilst the patient couch remains fixed in position laterally. In that embodiment, provision is made for the ion beam to enter the treatment room above the patient and to be deflected at various deflection angles by an ion beam deflection apparatus of fixed location, and that in turn deflects the ion beam towards the patient by means of the second ion beam deflection apparatus, which is displaceable on a sloping linear track. In that embodiment too, the apertures are small, because a symmetrical scanning unit is arranged downstream of the displaceable ion beam deflection apparatus and in turn pivotally follows the deflection angle of the ion beam.
In a preferred embodiment of the invention, the angle xcex1 of the sloping linear track is 45xc2x0. That sloping track at 45xc2x0 results in the fact that the patient can attain all irradiation angles in the quadrant of a circle from the side of the patient to vertical with respect to the patient, without the patient couch having to be moved.
For the purpose of deflecting the ion beam from the horizontal direction to a sloping track, the second irradiation system preferably has a first deflection magnet for the highly accelerated horizontal ion beam. A second deflection magnet, which belongs to the displaceable ion beam deflection apparatus, preferably directs the beam from the sloping linear track to a horizontal direction, and a suitable magnetic deflection system arranged downstream or a solenoid magnet causes further deflection between 0 and 90xc2x0 with simultaneous movement of the entire ion beam deflection apparatus in dependence upon the setting of the excitation current of the suitable magnetic deflection system or of the solenoid magnet.
A preferred embodiment of the first irradiation system provides a first deflection magnet for scanning the tumour volume in an X direction of the plane orthogonal to the central ion beam deflection region and a deflection magnet for deflection in the direction of the central ion beam deflection region in a Y direction of the plane orthogonal to the central ion beam deflection region with additional superimposition for scanning the tumour volume in that direction.
That embodiment of the first irradiation system has the advantage that no additional deflection magnets are necessary and most patients with tumours can be treated in such an embodiment of the first irradiation system having a restricted deflection angle.
The spacing between the deflection magnet in the Y direction, in the case of the first irradiation system, and the patient couch is preferably between 5 and 7 m. On the other hand, a spacing between the displaceable linear track of the solenoid magnet of the second irradiation system and the patient couch is preferably from 3 to 6 m, the symmetrical scanning unit, which is displaceable therewith, being arranged in that range between 3 and 6 m.
Where a lifting apparatus for the patient couch is required in one of the embodiments of the invention, it is also possible for the entire floor of the irradiation room to be raised together with the patient couch so that the patient still advantageously has the impression of being in a fixed position in a conventional treatment room and operational staff can treat the patient in a normal working position at any time before and after irradiation.
For measuring the position of, and monitoring, the scanning ion beam, the ion beam system preferably has, in each irradiation chamber, ionisation chamber measurement apparatuses and multiwire chamber measurement apparatuses. Those measurement apparatuses advantageously indicate both the intensity of an ion beam and also the location of an ion beam.
The entire ion beam system is so designed that, in a preferred embodiment, the irradiation systems are arranged in irradiation rooms that are themselves located compactly next to one another and in the shape of segments of a circle. That has the advantage that short ion beam paths, having few deflection magnets, have to be connected to the accelerator as the ion beam source. In addition, that arrangement advantageously allows expansion of the system at any time, should that become necessary later on. That results in a kind of radial construction of the entire ion beam system with a plurality of irradiation rooms as the optimum solution.
In a further preferred embodiment of the invention, the ion beam system is provided with a visual checking means for the patient couch in the irradiation room in order to monitor defined angle-of-rotation changes between various settings for multi-field irradiation. That visual checking means advantageously allows the co-ordinates of the patient system to be compared with those of the radiation room, and checked, after transfer to the irradiation position. Rotation of the patient couch, which may be necessary in the case of multi-field irradiation from various irradiation angles, can be controlled from the outside by means of the visual checking means.
In a further preferred embodiment of the invention, the irradiation system has locking apparatuses for taking up and positioning a patient couch in the irradiation room. Such locking apparatuses are mechanically complex devices which ensure that the patient couch is adjustable with millimeter accuracy in relation to the irradiation direction and the irradiation angle. The locking device moreover ensures complete coupling between take-up and positioning devices for the patient couch so that the ion beam can exactly scan the tumour tissue in the irradiation room.
A method of carrying out ion irradiation in an ion beam system of the present invention comprises the following method steps:
a) immobilisation of the patient on a horizontal patient couch in a preparation room of the ion beam system;
b) determination of the optimum irradiation angle for the irradiation therapy;
c) selection of the suitable first or second irradiation system;
d) adjustment of the deflection angles and the locations of the deflection apparatuses for the central ion beam deflection region;
e) moving-in, locking and adjustment of the patient couch relative to the predetermined optimum irradiation angle in an irradiation room;
f) carrying out irradiation, where appropriate with interruptions for changes in the position of the patient couch and/or in the deflection angles of the deflection apparatus for multi-field irradiation;
g) transfer of the patient back to an aftercare room; and
h) removal of the patient immobilisation.
In that method, the patient couch advantageously serves as a movable irradiation unit, that part of the patient which is to be irradiated being immobilised with respect to a mechanical carrier system. For that purpose, in the preparation room, the stereotactic system is linked to the patient and the position of the patient in relation to that system is verified, for example by means of X-ray images. That method step a) takes from 30 to 60 minutes per patient and is accordingly the most time-consuming part of treatment and, at the same time, requires highly qualified staff. For that reason, a plurality of preparation rooms are preferably provided per irradiation room. The transfer to the irradiation room that follows should not take a great deal of time. There, the irradiation unit, together with the patient, is mechanically locked into a given irradiation system.
After transfer to the irradiation room, the co-ordinates of the irradiation unit are compared with those of the irradiation room and checked; only then can the patient be irradiated. Any rotation of the patient couch which may be required in the case of multi-field irradiation can be controlled from the outside with the aid of the visual checking means preferably incorporated. After irradiation, the patient, together with his irradiation unit, is taken to an aftercare room and can be discharged after removal of the immobilisation.